The present application claims priority of Taiwan application Ser. No. 89114552, filed on Jul. 20, 2000, and the contents thereof are herein incorporated as reference.
1. Field of the Invention
The invention relates to an integrated dual-directional feed device, and more particularly relates to an integrated dual-directional feed device for receiving signals from two satellites in small angle.
2. Description of the Related Art
Due to rapid improvement of the high technology, it becomes more popular in signal transmission via satellites. In signal transmission via satellite, the coverage area of signal is wide; and the signal transmission path is not easily negatively affected by landforms. Therefore, there are more technique developments on signal transmission via satellite.
Now referring to FIG. 1, which shows signal transmission between a satellite and an antenna disk. The satellite 10 rotates around Earth in a synchronized orbit. When an RF (radio frequency) signal is transmitted from an earth station 12 to an antenna dish 14 for destination, the RF signal is transmitted to the satellite 10 first. Then, the RF signal is transmitted from the satellite 10 to the antenna dish 14. That is, in signal transmission, the satellite 10 is considered as a relay satellite.
There are a variety of usages on the satellite. The usages includes military affairs, direct TV programs, weather, Internet and so on. In home applications, the direct program system and Internet applications are most popular. For direct program system, the signal transmission between the satellite and the antenna dish is in single direction. In single-direction transmission, RF signals are mainly formed as circular polarized waves. However, in Internet applications, dual-directional transmission is applied, and RF signals should be formed as linear polarized waves so as to provide the bandwidth.
In direct program applications, a BSS satellite at West longitude 119xc2x0 transmits RF signals in circular polarized waves toward destination stations. In Internet applications, An FSS satellite at West longitude 116.8xc2x0 transmits and receives RF signals between destination stations. The BSS satellite is separated from the FSS satellite in a very small angle (2.2xc2x0) Therefore, in the same antenna dish for receiving signals from the BSS satellite and the FSS satellite, there must be a solution to separate the received signals.
The signals may be transmitted from the two satellites through two separate antenna dishes. However, it is high cost when using two antenna dishes. Some present antenna dishes are designed for receiving and transmitting signals between two or more satellites.
Now referring to FIG. 2A, it shows a conventional antenna dish. The reflection surface 22 of the antenna dish 20 is parabolic for focusing received signals onto the focus plane, and the signal gain on each point on the focus plane is above a predetermined level. A number of feed horns 25 maybe installed on the focus plane for receiving signals from a number of satellites.
For the conventional antenna dishes 20 for receiving signals from two satellites, there are two feed horns on the focus plane. If the two satellites, for example the BSS satellite and the FSS satellite in a 2.2xc2x0 angle, separate from each other within a small angle, the two receipt points on the focus plane may be close to each other. If so, the two feed horns 25a and 25b should be close to each other for receiving signals well.
In tradition, the first feed horn 25a and the second feed horn 25b are both located on the focus plane of the antenna dish 20. The first feed horn 25a receives circular polarized waves from the BSS satellite. The receiving band is about 12.2 GHz 12.7 GHz. The second feed horn 25b receives and transmits linear polarized waves between the FSS satellite. The receiving band is about 11.7 GHzxcx9c12.2 GHz, and the transmitting band is about 14 GHzxcx9c14.5 GHz.
Now please refer to FIG. 2B. Because the angle between the BSS satellite and the FSS satellite is so small, the respective receipt points for receiving signals from the two satellites are also close to each other. Due to this limitation, if the antenna dish is applied with a traditional circular LNBF (low noise block with integrated feed), the radius of the circular LNBF is limited. Accordingly, the communication quality is also negatively affected.
The circular wave-guide tube of the conventional LBNF should be large enough for obtaining enough gain in receiving signals from two satellites in a small angle. A large wave-guide tube makes the feed horn difficult to focus RF waves from satellites and the enlarged antenna dish is high cost. On the other hand, a small wave-guide tube reduces signal gain. It is an important issue to trade off between gain and area of the wave-guide.
One of the objects of the invention is to provide an integrated dual-directional feed horn for receiving RF signals from two satellites in small angle.
In the invention, the integrated dual-directional feed horn, for receiving RF signals from two satellites in small angle, includes a first LNBF (low noise block with integrated feed) and a second LNBF. The antenna dish focus the received RF signals onto receipt points of the focus plane, and both the LNBFs receive focused RF signals. Wherein, the first LNBF receives circular polarized waves from the BSS satellite and the second LNBF receives linear polarized waves from the FSS satellite. In the invention, for receiving RF signals from two satellites in a small angle, the distance between the two LNBFs is short and the area of the wave-guides tube should be large enough for better signal gain.
Therefore, one characteristic of the invention relies on integrating two LNBFs and making the two LNBFs adjacent to each other in the direction of short axis. Accordingly, the two LNBFs receive RF signals from two satellites in small angle. Increasing the length of the long axis thereof increases the areas of the wave-guide tubes. The signal gain and communication quality are obtained.